Initiation of Plate Tectonics from Post-Magma Ocean Thermo-Chemical Convection

TL;DR

This study uses physical models to show that proto-plate tectonics could have started on early Earth within 100 million years after magma ocean solidification, influenced by mantle temperature and atmospheric conditions.

Contribution

It introduces grain-damage based models demonstrating the plausibility and rapid initiation of proto-subduction on the Hadean Earth, a novel mechanism for early plate tectonics.

Findings

Proto-subduction was possible on the Hadean Earth.

Proto-plate tectonics could initiate within ~100 Myrs after magma ocean solidification.

High mantle temperatures lead to sluggish subduction modes.

Abstract

Leading theories for the presence of plate tectonics on Earth typically appeal to the role of present day conditions in promoting rheological weakening of the lithosphere. However, it is unknown whether the conditions of the early Earth were favorable for plate tectonics, or any form of subduction, and thus how subduction begins is unclear. Using physical models based on grain-damage, a grainsize-feedback mechanism capable of producing plate-like mantle convection, we demonstrate that subduction was possible on the Hadean Earth (hereafter referred to as proto-subduction or proto-plate tectonics), that proto-subduction differed from modern day plate tectonics, and that it could initiate rapidly. Scaling laws for convection with grain-damage show that, though either higher mantle temperatures or higher surface temperatures lead to slower plates, proto-subduction, with plate speeds of $\approx 1.75$ cm/yr, can still be maintained in the Hadean, even with a CO$_2$ rich primordial atmosphere. Furthermore, when the mantle potential temperature is high (e.g. above $\approx 2000$ K), the mode of subduction switches to a "sluggish subduction" style, where downwellings are drip-like and plate boundaries are diffuse. Finally, numerical models of post-magma ocean mantle convection demonstrate that proto-plate tectonics likely initiates within $\sim100$ Myrs of magma ocean solidification, consistent with evidence from Hadean zircons. After the initiation of proto-subduction, non-plate-tectonic "sluggish subduction" prevails, giving way to modern style plate tectonics as both the mantle interior and climate cool. Hadean proto-subduction may hasten the onset of modern plate tectonics by drawing excess CO$_2$ out of the atmosphere and cooling the climate.